<template>
    <ul class="list">
        <li class="item"
        v-for="item of letters"
        :key ="item"
        :ref="item"
        @touchstart.prevent="handleTouchStart"
        @touchmove="handleTouchMove"
        @touchend="handleTouchEnd"
        @click="handleLetterClick" >{{item}}</li>
        
    </ul>
</template>


<script>
export default {
    name: 'CityAlphabet',
    props:{
        cities:Object
    },
    data(){
        return{
            touchStatus:false,//标识
            startY:0,
            timer:null
        }
    },
    updated(){
        this.startY = this.$refs['A'][0].offsetTop
    },
    methods:{
        handleLetterClick(e){
            this.$emit('change',e.target.innerText)
        },
        handleTouchStart(){
            this.touchStatus = true
        },
        handleTouchMove(e){
            if(this.touchStatus){
                if(this.timer){
                    clearTimeout(this.timer)
                }
                this.timer =setTimeout(()=>{
                    const touchY = e.touches[0].clientY - 79
                    const index = Math.floor((touchY-this.startY)/20)
                     if(index>=0&& index<=this.letters.length){
                             this.$emit('change',this.letters[index])
                         }
                },16)
                
            }
        },
        handleTouchEnd(){
            this.touchStatus = false
        }
    },
    computed:{
        letters(){
            const letters = []
            for(let i in this.cities){
                letters.push(i)
            }
            return letters
        }
    }
}
</script>


<style lang="stylus" scoped>
@import '~styles/quanjubianliang.styl'
    .list
     display flex
     flex-direction column
     justify-content center
     position absolute
     top 1.58rem
     right 0
     bottom 0
     width .4rem
     .item
         line-height .4rem
         text-align center
         color $bgcolor
   
        

</style>
